Combined x-ray and fluoroscopic apparatus



July 26, 1949. L. MACKTA COMBINED X-RAY AND FLUOROSCOPIC APPARATUS "3 Sheets-Sheet 1 Filed Nov. 9, 1946 ass/1mm 94 E n/Irma:

VIDEO I flMPUF/fR July 26, l949.' 1.. MACKTA V COMBINED X-RAY AND FLUOROSCOPIC APPARATUS 3 Sheets-Sheet 2 Filed Nov. 9, 1946 I INVENTOK [e0 Afar/[f0 BYWA N 3 SheetQ-Sheet 5 L. MACKTA COMBINED X-RAY AND FLUOROSCOPIC APPARATUS QTW July 26, 1949.

Filed Nov. 9, 1946 INVENTOR Lev" fiariffa ATTORNEYS Patented July 26, 1949 UNITED STATES PATENT OFFICE COMBINED X-RAY AND FLUOROSCOPIC APPARATUS Leo Maekta, Brooklyn, N. Y.

Application November 9, 1946, Serial N0. 708,886

This invention has for its principal object the production of an X-rayfluoroscopic apparatus for permitting detection and visual inspection, for indefinitely long periods of time, of a normally invisible object or entity, such as a fractured bone or a foreign object in the body, or hidden defects or internal flaws in an object such as in a metallic shaft or the like, without injury to the patient, operator, or others, who ordinarily might suffer injury when subjected to the deleterious effects from overexposure to the intensity of an X-ray beam. The results achieved by means of the invention, accordingly, are equally enicacious when the invention is practiced either in the field of medicine and surgery or industrially.

A further object of the invention is the production of an X-ray fluoroscopic apparatus of the character above described which may be effectively operated with a current of relatively small volume to thereby obviate danger of overheating of the X-ray tube and adjacent parts and to minimize the expenseof operation.

A further object of the invention is the production of an X-ray fluoroscopic apparatus so con structed and so operating as to permit continuous visual inspection of the image of the object examined in daylight or under normal room lighting, as in an operating room, without necessitating the adaptation of the operators eyes i to the existing light and to thereby facilitate surgical removal of buried foreign bodies or the setting of fractured bones.

A further object of the invention is an improved method of practicing X-ray fiuoroscopy whereby the above and other desired results may be achieved.

A further object of the invention is the production of an X-ray fluoroscopic apparatus of the character described which may be portable and easily adapted for field use because, among other things, of the substantial reduced transformer power required for the X-ray tube and the consequent decrease in the weight of necessary equipment ordinarily required in X-ray fiuoroscopy.

Still a further object of the invention is the provision in an apparatus of the above character of a movable gas counter tube the movement of which is synchronized With the vertical reciprocating movement or frame rate of the scanning mechanism employed thus enabling the use of a much smaller counter tube than ordinarily would be necessary.

A further object of'the invention is the inclusion in an apparatus of'the above character 12 Claims. (Cl. 178-63) of means for expediting the deionization of the counter tube immediately after each ionizing event occurs to thereby enhance the efiiciency of the tube and render it capable of operating with suflicient rapidity to enable it to keep pace with the operation of the scanning mechanism in the organization of the elements of the invention.

Further and other objects and advantages of the invention will appear from the accompanying description, the invention consisting in the novel X-ray fluoroscopic apparatus and method of practicing X-ray fiuoroscopy hereinafter more particularly described and then specified in the claims.

In the accompanying drawings illustrating a practical embodiment of the invention:

Fig. 1 is a perspective view of the apparatus with its accompanying electrical operating and synchronizing circuits.

Fig. 2 is an enlarged perspective view of a modification of some of the parts of the apparatus.

Fig. 3 is a perspective view of the X-ray tube.

Fig. 4 is an electrical diagram of a modified circuit for the gas counter tube, such as that of the Geiger-Mueller type, functioning as a uniform pulse generator operating on a voltage exceeding that of the threshold voltage.

Fig. 5 are diagrams showing the characteristic curves of the phase relationship between the counter tube applied voltage, the X-ray beam intensity and the plate voltage of the thyratron tube, when the apparatus operates according to the modification of Fig. 4.

Fig. 6 is an electrical diagram of a modification of the circuit of Fig. 4.

In practicing the instant invention, advantage is taken of the extreme sensitivity to X-ray radiations of a gas counter tube such as that of the Geiger-Mueller type, permitting it to detect and record the densities of the elements of an image created by an X-ray beam penetrating a normally opaque object or entity. The passage of this X-ray beam into the sensitive volume intermediate the electrodes of the counter tube will be manifested in the form of a succession of electrical impulses produced by abrupt changes in voltage of the central wire or anode of the counter tube brought about by successive ionizations of the gas contained in the tube. The electrical impulses so produced subsequently are re created, as will be presently described, in the form .of visible light areas corresponding to the 55 elements of the image of the object studied,

which permits continuous visual inspection of the image.

According to the invention, also, the invisible object or entity examined is at no time subjected to the full intensity of the X-ray beam but to a single ray only of said beam at any given instant or fraction of an instant of time and the penetrating rays are projected through the object examined in very rapid succession both vertically and laterallyahd immediatelyadjacent to each other over a predetermined area to initially create an invisible image of the examined object. The method employed simulates somewhat the mechanical horizontal and verticalscanning of the reflected light rays of the elements of a visible entity as received by a photoelectric cell or similar detector and as utilized in a television type receiver, the distinction being, 'li'd'weventhat in the instant invention the repeating action is provided for the individual penetratng rays or radiations of an X-ray beam generated by an X-ray tube and projected from its-targetthrough the invisible examined object. .In T the television apparatus, the normally opaque object examined is not interposed between the scanning device and the light detector as inthe present easaiwhere a gas counter tube-is placed behind the examined object.

v Referring in detail to the drawings:

The vertical'and horizontal members of any suitable typed-supporters indicated at to and l I respectively, 'Fastenedto the--vertica1 member I is anrangledsstmt 1:2 -w,li:ic h-rigidly carries a shield t3 comprising;anwopadue-plate composed of a lead-like material impervious to the passage therethrougl'i of the: mys of an 'X-ray beam generated by a conventional X-ray tube I i shown more clearly .in--;Fi-g-. 3. 1 SQJidrtHbl-E is positioned adjacent the plate 4% s rides-provided with the usual heating cathode IS an anode; or target Iii, preferably of tungsten, as ell as the focusing cup -or ;eyli nder "f l for confining ,the electrons emitted by the heating cathode within a limited area and for directing them: against the inclined face "of; the anode taiiget -16 --w hichin turn generates the X-rays and-directs the beam thereof tangentially in the-direction ct -an aligning rectangular: aperture or: opening 11' in the vertical plate 'I 3 through which-aportion of the primary rays o f the 'b'eain pass. -'Ihe' -target spot of the anode l5 isfthe' radiant pointrof the conical beam or pencil arrays ;generatedby .the x ray tube so that any given ray of that beam originates at that point. H W

'The heating cathode I E- and anode iii of the X-ray tube are connectedpto-suitable insulated conductors [8 which maysupport the tube and which in turn are. supported-:bya bracket 19 fastened to the'strut' 12. Said conductors -l 8 are connected to a source'gof high voltage well filtered direct current, (notshown) and-having, for most purposes, apoter'itial of ;irom"7 5,000 to 100,000 volts. Because.oflthesensitivlty of the gas counter tubeemployed' inthe, system of the invention, however, the yolumeotcurrent could be as low as 5 milliamperes' instead of to 100 milliamperes usuallyrequiredin- X-r-ayfluoroscopy and radiography. -It is important nevertheless, that the currentlbe well-filtered as any voltage ripple will result ina vcorrespending.ripple in the X-ray radiations which afireimpressed on the detecting instrumentalitiesof the system and will finally manifest themselves :as distortions in the i image of :the-object-orgentity examined.- Because of the small X 'ray tube icurrent required; adequate rec- 4 tification and filtering of the high voltage current should not be diflicult.

A rotatable drum composed of a lead-like'material opaque to X-rays is indicated as 20. Said drum is provided with a plurality of pin-holes 2i in the annular Wall thereof which are equally spaced from each other and from the upper peripheral edge of the drum. Said pin-holes 2i are positioned so as to :be in :alignment'awithwhe target spot of the anode 16 of the iX-rray tube and with the rectangular aperture 11 in the shielding plate id as the annular wall of the drum revolves around the drum axis whereby a single ray of the X-ray beam, "represented in dotted lines for instance at 22, passes or is projected through one of the pin-holes at any given instant and through the object or entityv being examined which for clarity of "description only is here represented as theloWer portion of a leg 23 of a person. No precise number of pin-holes 2| is necessary as the number may vary .to :suit varying conditions.

The drum 5 iilfljustrdescribed is rotated by a .conventional motor indicated diagrammatically at 24'the motor shaftof whichis.connectedatoaconventional .re'ductionwgear .andrightsangled -,drive a second gear box indicated lat-2 8 -whichemechanism is also conneeteditoeaahorizontally extending rotatable shaft. 29, .carrying ta .oam;-30. is fixed thereon. .Thelcomigurationvofrthezperipheral edge of said camis bestillnstratedrin:Eig. 2 with its lowermost pointh-indicatedcat 3.0:. :Saili edge tan y ri ag s'a roller 3t icurnallcdin the arms "of a biiacleetedz which iisiastenedstosventical member to act, he u portppreviouslyxree ferred to.

A U-shaped bracket;is-.z-indicated at33raaridds fastened" torthe gean hoxe25 rand 'locselycreceives the rotatable drumlshaitiit thereth-rough. isai'd bracket 33 is providedxwithupwardlyt extending parallel arms s i. additional-azbracketifor pivotally supportin 'Hheleentire idrumeand motor assembly is indicated .atfiflzandziszb OltEdBOIL other- Wise secured to the vertical memberoisil. .ctSaid supp orting bracket is. ;providedfwithvoutwardly extending supportinggarmszifiiwhichrareipivotally connected,1.as by pins ,ori:pivots-;:3 l,:to the ,upper ends of' arms 34, the pivoted-connections bein such that the..lo-ngitudinaltraznsxofirthe spivcts'zisl are in horizontal aalignmentrwith -the; itargetspot of the anode: 4510f :thes'xz-ramtulae.

A disc commutator::is;:iniiicatedLatBB. I :is carried by and Zrotateswi-th.-;the-.adrum shaftifle and it is the rrevei'sezofi-aavcqnventional lpcommutator in that: electrical. contact .isrma-de with :the smaller of the-.contact seem nts#-.3fi:en=.its periphery rather than yvithetheiiintermediatebroade segments 30" Which-tare nomposednofean insulating material. .Thapumbercof --contaic tqs egments, 3-9 equals the number of pin-holes 2| inthe wall of the drum-- 20 andsaid segments @arereon-nected together @by iar-condllotiilg rlngi41which; in, turn arr/e07,

is connected by conducting wire 42 to a metallic. slip ring or collector 43 carried by but insulated from shaft 26. A contact strip or brush is indicated at M. The free end of said contact strip engages and makes slidable contact with the slip ring 43 while the other end is connected to one of the arms3l of bracket 33. A second Contact strip or brush is indicated at 44' and is provided adjacent its free end with an angled contact member 45 adapted to successively engagethe contact segments 39 as the commutator rotates. The oppositeend of said brush 44' is connected to but insulated from the other of the arms 34 of bracket 33.

A tension spring is indicated at 46 audits ends are attached to an arm. 34 of. bracket 33 and a supporting arm 36 of bracket. 35 and it acts to swing the entire suspended drum and motor as semblyon pivots 31 and in the direction of Ver of the cam til; Asolenoid. 41 has also been provided for apurpose to be described. It is supplied.

withthe usual external winding 48 and it is fastened to the horizontal support by a U-bracket $9. The movable core of said solenoid. is tapered and is indicated at 5d and it is held and supported by a strip El fastened to the gear box so that a free reciprocating movement is imparted to said core within the solenoid to change the inductance of coil 48 when the drum and. motor assembly oscillates or rocks on its pivots 31.

The degree of rocking or oscillationof. the drum and motor assembly on pivots 31 is relatively small, the amplitude of: oscillation being deter mined by the height of the: aperture IT in plate l3, that is; the distance between the horizontal walls of said aperture which distance also defines the limits of the relative vertical position of any given rayof the X -ray beam passing through. said aperture. A forward pivotal movement of the drum and motor asseinblyoii pivots. 31' is brought about positively by engagement of. the: high side of the edge of the cam 3!! with roller 3l' while a reverse movement in the opposite direction to swing the drum and motor assembly towards the vertical member It] is effected partially by the action of the spring 45 when roller 3! engages the lowermost point iii ofthe cam edge. The motor and drum assembly is shown in approximately neutral position in Fig. 1 and each cycle of a complete oscillation. onpi'vots 31. may be. referred. to hereinafter as the frame rate of the vertical scanning operation.

The relative ratio of the gears in gear box 25 is such that approximately 150 pin-holes" 21 are brought into alignment withi'aperture ll, each for passage of a single ray of the X-ray beam therethrough, during each. cycle of oscillation of ment of the pin-holes withrespect to the aperture l'l' through which the lei-ray beam is. projected may be referred to asthe hor-izontal scanning operation. The relative: ratio of the reduction gearsin gearbox 2 8 is such that the drum and. motoirasseinbly, because... of thel action of the cam;

containedi'n the tube is one which produces a large yield of ions when subjected to the ntensity of the rays of an X-ray beam or the hardness commonly used for radiogiaphy and nuorosco y. A mixture of argon and ether is suitable for the purpose although other gases or mixtures thi'eiif may be used effectively. The cathode 53 or the counter tube may be ofbrass and is the form of a. cyllfidl or Siiii- G-IJlifldi htili ifi'g Elijctfi area facing the X-ZQSI balh 6f a size so ii include Within it the area of radiation as measured and defined by the piii-holes'fl and the site of the aperture opening I'I". The some or tea tral wire 54 of the counter tube may beef sten. It extends lbnlg'itudiilahy or the tube fiifl is concentric with the longitudinalai'ris ofthe cath ode 53. Th en'iflpe 6f the tube may be (if the typeof glass or aluminum 'metal which will readuy permit the passage of X iay radiations therethrough Withmaiii'riilm" ifii'elioyf In some cases where a counter tube of relatively small size is employed it will be found 'd' sir'able to reciprocate it vertically and synchronou'sly with the rocking or frame movement of the drum 20 to insure that the penetrating rays of the X-ray beam will not escape entering the Sensitive region of the counter tubeas th oii'iiti tube then will follow the Vertical scanning -615erition.- A mechanism for efifecting a mcvem nt of this character is illustrated in Fig. 2m w has: indicates a tube-carrying frame, the vertical orside' members of which nave the upper and lower shafts 56 and 5'! respectively journalled theiein... on their outer ends, said shafts carry u per and.

1ower rollers 53 and 59 respectively, each pair of rollers being connected together by an endless belt 60 which is held taut. Each beltcarriesj a block 6| provided with a strap or clip 6-21 for supporting the counter tube 52'. The lower shaft 51-carrles a bevel'gearfi3 meshing with a bevel. gear 64 the vertical shaft 65 or whichl's jou naued.

in the lower horizontal wall of the frame 55.

The strip 5| previously described may be pro vided with a right-angled extension 66 carrying a curved rack 61 whose r'adius of curvature is concentric with the longitudinal ai'c'es' of pivots s1, s'aidr'ack meshingwith apinion at whose shaft. 69 is journalled in a bracket 1-D which maybe fastened to the horizontal member I I. A flexible drive shaft H is supported by a bearing member l2 and connects shafts 65' and E9 so that-as is obvious, rocking or oscillation or the drum 20: on its pivots 37 effects verticalsynchronous re ciprocation of the counter tube 52'. mantle-nee: trical conductors I3 and M are connected to the wire and cylinder of the counter tube to in sulated binding posts and thenceto the cit i the counter tube by successive ionizatio'ns or the gas therein. to generate electrical impulses con or them forming-yto the elements or the i g p Visible object examined, as a boneiii thelg '23;

I of the mixer tube.

by the rays of the X-ray beam, produces a voltage drop across the high resistance TI. The voltage is impressed on the control grid of a suitable pentode mixer tube is through a bias battery 19 which brings the voltage on the control grid to a desirable Value for the operating characteristics A conventional carrier frequency oscillator having a frequency approximating 100 kilocycles is indicated at'fiii. and is electrically coupled to the second grid of the mixer tube '58 through a condenser 8 l A high resistance is indicated at 82 and is included in the return circuit for the oscillator and grid current, its purclose to the Geiger-Mueller counter tube as is conveniently possible. Said preamplifier acts to bring the level of the signal output of the counter tube 52 .to a value where it may be transmitted over the convenientlylong coaxial transmission line 85 to be amplified and viewed on a fluorescent screen as will be presently described. 7

r The output of the preamplifier as obtained from the coaxial transmission line 85 consists of ;a modulated signal of a frequencygenerated by the oscillator as, the 'modulations being those impressed on the mixer tube 78 by any variations in the ionizing current in the counter tube 52. Variations in the ionizing current in the counter tube occur from variations in the intensity of the rays of the X-ray beam as they scan the different radiodensities of the entity 23 under examination. The coaxial transmission linedii terminates in the input of a conventional broad band amplifier 86,. preferably of the video type, having a ire" quency range manytiines that of an ordinary amplification system. Said broad band amplifier 85 amplifies the signals receved by it to a do sirable level and feeds these signals to a. conventional second detector circuit which is direct coupled to another stage of amplification for com trolling the intensity grid of a cathode ray television type tube This detector and amplifier is indicated at 8? and the cathode ray tube at 88. The function of the detectorand amplifier a: is to eliminate the carrier frequency and torecreate the shape of the impulses generatedby the counter tubefEiZ. Said cathode ray tube 88 is provided with the usual fluorescent screen "89 on which the image of the object examined is made visible. The phosphor on said screen is of the per= sistent type, the duration its persistence being determined by the frame or vertical scanning rate previously referred to. I

V The-sharply focused beam of electrons modulated in the cathode ray tube 88 by the impulses of impulses forira'me' or vertical synchronization are derived from the changes of impedance of coil Q8 ofsolenoid 41 brought about by the reciprocation of the tapered .core 5!! in said solenoid when the drum :and motor assembly oscillates on pivots3'l.

A resistance 92 and battery 93are connected in series 'with'the brushes 44 and 44'. At each instant one ofthe segments is engaged by the contact brush it a Voltage is developed across said resistance 92 to trigger or synchronize a conventional relaxation oscillator indicated at 94 which generates a voltage having aJsaw-tooth wave form which is impressed on the horizontal deflecting, plates SI of the cathode ray tube 83.

For the frame or vertical synchronization, a source of alternating current 95 is provided whose frequency is in the neighborhood of cycles or higher; This source of current is connected to the winding 'o'nthe sole'noidl. and to a transformer 9.6.. The current in. the primary of the transiormerjis then'varied as a result of the change in the impedance of the solenoid by virtue of the movement of its core therein. Said core 59 is so 7 tapered that the final voltage which will be shown tobe applied across the vertical deflection plates 5% of the cathode-ray oscilloscopetube' 88 varies indirect proportion to the angle of oscillation of the drum 25 on its pivots 3?. V

The. alternating current: voltage developed across the secondary of transformer 96 is rec'- tiiied by a conventional bridge type rectifier 9'3 and the rectified voltage is filtered by a, condenser 981110. eliminate the usual ripple. The combination oi the condenser 88 and a resistance 99 has a period such that the voltage across the deflectionplates 99 will closely follow the variations of volt age brought about by the movement of the iron core. 56, yet will efiectively filter the higher fre duency'ripple set up by'the source of alternating current. The voltage thus produced across resistance 99 is applied to the vertical deflecting plates 7 Bilof the cathode ray oscilloscope tube 88 through the counter tube in the-manner described is deflected vertically and horizontally by its conventional pairs of vertical and horizontal deflecting plates 9d and at respectively by changes of volt a battery its which corrects the voltage to a proper value to center. the neutral position of the electron beam on the screen 89 of the oscilloscope.

The inode of operation of the apparatus will be apparent to one skilled in the arts of electronics and television. The rays of the electron'beam in the. cathode ray oscilloscope 88 scan the fluorescent screen 83 of the tube synchronously with.

the scanning of the penetrating rays of the X-ray beam through the invisible object being examined. The spacing of the pin-holes 2i in'the drum 2% r f is such thatras any given pin-hole passes beyond the limits of the X-ray beam as defined or restricted by the width of the aperture H, the next succeeding pin-hole just enters the opposite limit of the beam. For the vertical scanning operation,

.the diameter of the pin-holes is such that the individual rays of the X-ray beam passing through successive pin-holes just touch or impinge on each other as the. scanning operation proceeds. It.

willbe noted also that in both'the horizontal and --vertical scanning, the longitudinal axis of the when the apparatus-is used in surgery for in imity to the drum mechanism.

stance, cause similar variations in the ionizing current in the Geiger-Mueller counter tube 52. These current variations are then amplified in such manner as to control the intensity of the electron beam in the oscilloscope 88 resulting therefrom and which illuminates the fluorescent screen 89 of said oscilloscope tube and permits visual inspection of theimage of the entity examined on said screen. Since the phosphor of the screen 89 is persistent for the duration of a frame, the image will remain constant on the screen for each frame and will be recreated for the next succeeding frame. There will be a blending of the old and new images thus created to exhibit a smooth change even if the examined object is moved slowly. The fluorescent screen may be illuminated brightly by the employment of a high accelerating voltage for the beam in the oscilloscope tube and the diameter of the screen may be varied to suit ones convenience.

Should the apparatus be used for exhibiting the image of the object examined to a large audience, a plurality of cathode ray oscilloscope tubes may be connected to the output of the video amplifier and to the synchronizing circuits to reproduce the image of. the object examined at a number of separated places. Furthermore, a photographic film or plate may be placed against the screen of the cathode ray tube to photograph the image, or

a camera may be focused on the screen for the same purpose. H Shouldit be necessary to inspect a relatively small portion of the invisible object examined with more detail, that can be accomplished by positioning the object in closer prox- When the apparatus is employed for surgical manipulation, such for instance, as the reduction of fractures or foreign body removals, the patient, surgeon and others are free from danger of overexposure to the X-rays as it has been estimated that the total radiation passing through exposed tissue will approximate 2 10- that which would be required for ordinary X-ray fiuoroscopy. The number and size of the pin-holes 2i employed, the size and speed ofrotation of the drum 2|! and the size of the reduction gears and cam mechanism obviously may vary to meet varying conditions but it is desirable that the characteristics of the parts be such as to give the substantial equivalent of 150 to 200 line scanning at one frame per second. i

The operation of the apparatus has been described when the Geiger-Mueller counter tube 52 plying a reversed voltage to the counter tube during part of the cycle to sweep up the positive ions collected about the central wire 54 of the counter tube formed by the avalanche process upon the occurrence of an ionizing event and return them a relatively short distance to the wire. The firing rate of the counter tube, accordingly, is considerably accelerated. By employing this reversed voltage the number of scanned lines per second of the invisible object examined may be increased to give more detail to the image of the object and theframe rate may also be increased to follow rapidmotions of the examined object. Most of the other previously described components of the apparatus such as the drum and motor assembly, synchronizing circuits and oscilloscope tube are identical in this alternative method, the operating circuits of the X-ray tube and counter tube only being modified.

With reference to Figs-4 and 5, the X-ray tube id is supplied with high voltage from a conventional transformer llll, rectifier tube I62 and condenser I03. In addition, a saw-tooth Wave generator H34, preferably operating on a frequency of 2D kilocycles or higher, is employed which is electrically connected to the focusing cup or cylinder ll of the X-ray tube, the configuration of the wave generated by said generator it! being indicated at N to the right of that element. The cross-sectional density of the stream of electrons or the electronic beam emitted from the heating cathode of the X-ray tube changes rapidly and intermittently to follow the saw-tooth wave Hi5 andthe width of said operates as a proportional counter having an operating voltage across the counter which generates a pulse size proportional to the number of ions formed in the initial ionizing event. It may be desirable in some cases, however, to operate the counter tube in the Geiger or the most sensitive region of operating voltage and in which the size of the pulse is independent of the number of ions produced in the initial ionizing event. When operating in the Geiger region, the amplification of the counter tube isincreased considerably.

According to the method to be described and when the counter tube operates in its Geiger or most sensitive region with its voltage exceeding that of threshold value, graded variations of brilliance of theimage of theinvisible object examined may be obtained on the fluorescent screen of the cathode ray} oscilloscope irrespective of the all or nonef-character of the discharge in thecounter tube, Additionally, ,means are em; p o ed w ei b l the} are iiteqi cricy res se of the counter tube is considerably increased by apbeam striking the anode target; 16 changes periodically from a wide beam to a sharp one because of the variation in voltage applied to the focusing cup I! of the X-ray tube although the total current remains substantially constant. As the width of the electronic beam varies, the area of the target spot of the anode target it varies proportionately to thereby vary the intensity of the X-ray beam produced by each point of the target and thus increase or decrease the intensity of that beam and its individual rays which are projected through the pin-holes 2!, through the object examined and into the counter tube 52. This comes about because a relatively small portion of the focal point of th target is the source of any single ray of the X-ray beam which passes unobstructedly through and is confined by any given pin-hole at any given instant. The efiect, accordingly, is the production of an X-ray beam the intensity of which varies periodically and rapidly from a relatively small value to a relatively large value many. times during the scanning of a single line of the invisible object examined. In practice it willbe found desirable to adjust the total X-ray tube current so that the amount of radiation projected into the counter tube 52, after penetration, for instance, of an examined object of'medium radio-density, such as a small bone, is sufficient merely to cause the counter tube to discharge when the X-ray beam has avalue about mid-way between its minimum and maximum intensity.

For supplying current to the counter tube 52 in the modified apparatus it will be found desirable to employ a common square Wave generator Hit connected so as to produce a stronger negative pulse as compared with the polarity and voltage or thebattery Ill! so that its voltage output resembles the. shapeot graph lll8 shown at the right of. thatfllmen Thetotal action of battery I91 andthesquare wave'generator [06ins'ity in transit throughout the sweep only by the density of the object, means for rotating said scanning mechanism and means for oscillating the same. i

3. In an apparatus of the character described, a source of a beam of X-rays, a gas counter tube, scanning mechanism for scanning an invisible object interposed between said scanning mechaism and said counter tube, said mechanism being mounted to both rotate and oscillate thereby providing a two-dimensional beam sweep and said gas counter tube being mounted to have transitional movement in one dimensional direction of the scanning sweep, means for rotating said;

scanning mechanism, means for oscillating the same, and means connecting the scanning mechanism and gas counter tube so as to impart transitional movement to said tube synchronously with movement of the scanning mechanism in the said one dimensional direction.

l. In an apparatus of the character described, a source of an X-ray beam, a gas counter tube, scanning mechanism positioned intermediate said source and said gas counter tube, said mechanism including a member having a circular series of holes therein around said source for successively receiving individual rays of said beam therethrough and said member also being so mounted as to both rotate around and to osoillate with respect to said source, a shield interposed between said source and said member and provided with an opening therein to limit the cross sectional area of said. beam in its path from said source to said member, means for rotating said member to pass the holes thereof 5. In an apparatusof the character described,

source of an X-ray beam, a gas counter tube,

scanning mechanism positioned intermediate said source and said gas counter tube for directing individual rays of said beam through an invisible object and into said counter tube, said scanning mechanism including a rotatable drum substantially concentric with said source of X-ray beam and having pin-holes therein for successively receiving individual rays of the aforesaid beam therethrough, said pin-holes being equally spaced from each other and from an edge of the drum and positioned in alignment with and in a circular series around said source of the X-ray beam, means for rotating said drum, a lead-like shield interposed between said drum and source and provided with an aperture therein in the path of a predetermined arcuate beam sweep from said source to said pin-holes, and means for imparting a rocking movement to said drum synchronously with its speed of rotation.

iii)

fluorescent screen and a cathode ray gun and focusing control electrically connected with said counter tube for providing a cathode ray beam varying in intensity to accord with the intensity of the X-ray radiations received by said counter tube, deflecting plates insaid cathode ray tube having electrical connections with said scanning device, and means associated with said scanning device for electrically varying the plate potentials of said cathode ray tube through said electrical connections in predetermined accord with the rotation and oscillation of said scanning device.

7. In an apparatus of the character described; a source of an X-ray beam, means for periodically and intermittently varying the intensity of said X-ray beam, a gas counter tube of the Geiger- Mueller type, an annular member concentric with and rotatable around said source of X-ray beam and mounted to oscillate on a pivot Whose longitudinal axis is substantially parallel to said counter tube for successively directing individual of said beam both horizontally and vertically through an invisible object to create an invisible thereof and to produce successive ionizations of the gas in the counter tube conforming to the elements of the invisible image, means for rotating said annular member and means for oscillating the same. l

8. In an apparatus of the character described, an X ray tube for generating a beam of X-rays and comprising a cathode, an anode target and a focusing cup for directing the electrons emitted by said cathode to said anode target, means for supplying electric current to said cathode and anode, a gas counter tube, scanning means between said X-ray tube and counter tube for successively directing the rays of said X-ray beam through an invisible object and into the counter tube to produce successive pulses in said counter tube conforming in intensity to the elements of an image of the invisible object, electronic means electrically connected with said counter tube for recreating its output into a visible image of the object, and means for supplying a current of varying voltage to the focusing cup of said X-ray tube to thereby vary the intensity of the X-ray beam.

,9. In an apparatus of the character described, a source of an X-ray beam, scanning mechanism having a member adapted to both rotate and oscillate for successively directing individual rays of said X-ray beam through an invisible object both horizontally and vertically to create an invisible image thereohineans for rotating said member, means for oscillating'rthe same, a gas counter tube in the path of said rays through the object for detecting the elements of the invisibleimage so created and for generating electrical pulses conforming to said elements, a source of high voltage direct current connected to the electrodes of the counter tube, a preamplifier including a carrier frequency oscillator and a pentode mixer tube coupled to the source of high voltage and one of the electrodes of the counter tube, a broad band amplifier having a high frequency range connected to and for receiving the ouput or said preamplifier, a carrier frequency eliminator coupled to said broad band amplifier for eliminating the carrier frequency transmitted thereto by the amplifier, a cathode ray tube having an electron gun coupled to the carrier frequency eliminator for recreating the output of said eliminator into an electronic beam conformingztdthe'a 'pulses generated: by said counter tub e, fluorescent screen-for said cathode ray tube opposite said' -gun, and" deflecting. plates in said cathode'r'aytubewith onepair thereof electrically connected; to said-means I for rotating said mem-= ber'and another pair connected to the means for oscillating-. said member for directing the rays of said electronicbeam: to. said fluorescent screen synchronously with-the. vertical and horizontal movements of said sca-nning' mechanism.

In an apparatus of-the character described, Y-raytube-for generating: a beam of X-rays and'providedrwith the usual cathode and anode target, means electrically connected to said X-ray tube for periodically varying the cross-sectional dehsity'orthestream-of electrons emitted by the cathode to vary correspondingly the intensity of the X91336! beam; n'oe'ans in the path of the X-ray beam for projecting: individualrays of their -ray beam progressively through an invisible object to create an'invisible image thereof, a gas counter tribe in 'thepath of s'aid' individual rays for detecting' the elementsaofqthe invisible. image and for producing .asuc'cession of electrical pulses conforming in intensity to:the elements of said invisibleimage; a: generator connected to and for applying a voltageof intermittent reverse polarity to said gas counteritube for increasing its pulse frequency response synchronously with the variations in the intensity of the X-ray beam, amplif'yi-n-g'means connected to the output of said gas counter tube-ion amplifying thes'ame, and means connectedto'saidlampliiying-means for recreating 7 its pulseicfrequen'eyj response? synchronously with said amplifiedoutput in'toaa visible image cona forming to theaior'esaid invisible image.

i 11. In-an: apparatus oithe-character described, source of an X-ray' beam, means connected to-said source-for periodically varying the intensity of said beam, means in the path of said K-ray beam for projecting. successive individual ray-soi saidbeam through an invisible object to create an invisible image the a 6011111761" tube in the path or said'individual rays for detecting the elements of the invisible image and for producing a succession of pulses conforming intensity topth'e elements of said invisible image; a generatorconnec'ted to and for applying voltage of; intermittentzreverse polarity to said gas counter tube for increasing its pulse frequency response synchronously'with the variations in the intensity of theX-ray beam, a capacity resistance bridge connected to said generator and counter tube, means connected with and for amplifying output, of said counter tube, a thyratron coupled tosaid amplifier, and means connected with and: controlled by said counter tube for recreatingthe output of said thyratron into a visible image conforming to the aforesaid invisible image; a

1-2. Injanappa'ratus: of the character described,

a: sourcee ofi arrzxn-ray beanie. means; connected-t with saidri:sourceefor:periodicalmvarying thedne tensitygiofzsaid' beam-emeans: in'zthezpath OffSELid' beam for directing successive individualrays'of beam throu'ghian; invisible; object 1 to create an 1 invisible: image: thereof, ,a .gas counter". tube the variations;imtheintensity:of:theiXrray beam, an amplifiers: connectedi with: andiifor: amplifying the output'of: said-1 counterv tube, a ,thyratron coupled torsaid amplifier; means; connected with and for applying; agvarying. plateavoltage to said thyratron synchronously Withiv the: variation. in the: X-ray beam: intensity, .andimeans connected through: said: thyratrointov said counter tube for recreating the output: of said: thyratron intoa visible: image: conforming: to: the aforesaid invisible image: a LEO MACKTA.

B'EEERENGES: CITED The following references are of' record in the file" of" this patent; I

UNITED STATES PATENTS Humbert Name Date 1 ,548, 68? HOKie NOV. 8', 1927' 9,661,603 Dauvillier; Mar. 6,1928 1,730, 976' Jenkins Oct. 3', 1929 1 ,838,537 Dauvillierz, Dec. 29, 1931 113335393 Schmid1ing: Oct. 31, 1933 1,9 5,607 Herd'man- Feb. 6, 1934 19611713 Similar; June 5, 1934 1,912,221; Eulen'hofer Sept. 4, 1934 1,977,380 Ellis Oct. 16, 1934 2,048,094 Applebaum July 21, 1935 2,101,976 B'laclrwe'll Dec. 14, 1937 2,133,776 Bender Oct. 18, 1938 2,149,292 Hogan; Mar. 7, 1939 2,111,536 I Bi'ngley Sept. 5, 1939 2,234380'6 Ploke Mar. 11, 1941 2257-1774 VonArd'enne Oct. 7, 1941 2,274,341 "Mathes- Mar. 3, 1942 2315,576- Fearon Apr. 13, 1943 23319712 :Williams- May 18, 1943 2,349,225 scherbatskoy May 16, 1944 2,368,532 Fearon Jan. 30, 1 945 2,402,091} S'chade June 11, 1946 OTHER 'Pvnennnnonsf' Electron and Nuclear Countersfby Korff, Apr. 1946; pages; 4;; 5,163; T77; 

